php - Can't make cookies expire -

i'm trying make cookie expire, i've saw code it, , i've done already.

so, i've done making expire date time() - 10 make cookie time limit expire immediately, can't seem make work.

$number_of_days = 30 ;  $date_of_expiry = time() + 60 * 60 * 24 * $number_of_days ;  setcookie( "userlogin", $user_hash, $date_of_expiry, "/" ) ;  

this should work:

setcookie("cookie_name", "", time()-3600); 

if not work, have output before, have call before echo or html output. otherwise headers sent , can't change cookie information.